what determines the “slipperiness” of a material



E.g why is saliva more slippery than water or oil more slippery than water

In: Chemistry

Liquids make a surface less rough, removing much of the friction in the process. Without friction we have no “grip” on the surface and therefore slide more on it.

Two things can contribute to this. First the smoothness or lack there of. the smoother the surface the less friction aka slipperiness. The second source of slipperiness is chemical/molecular. Image I put a ton of small ball bearings on the floor. This would make the floor more slippery. Why? Because there is now a relatively free moving thing between you and the floor. The ball bearings are free to slide around making it very hard for you to gain traction. The same is true of water. The water molecules are relatively free to move around making hard for you to gain traction. This gets to why oil is more slippery. water is a very polar molecule. Google “polar molecule” a picture of water will be the top result. This allows the oxygen of one water molecule to be attracted to the hydrogen of another. Oil is non polar so it’s molecules are much less attracted to one another so they are much more free to slip and slide past each other. Think of it as if the water was small round magnets on the floor while the oil would be the non magnetic ball bearings. Both would make it harder to walk but the ball bearings would be worse.